1. The Field of the Invention
The present invention relates to an apparatus for determining the location of a line object lying on a tablet by detecting electromagnetic induction between the positioning coils corresponding to that line object and the grid-shaped conductors formed in the grid structures of the tablet, and to an apparatus for tracing and recording the movement of the line object on a tablet, and in particular to a method for compensating positioning errors resulting from the displacement in between the positioning coils and the line object. This invention also relates to an image scanning system which offers a capability of image scanning and position determination. The position compensation method, which is used to offset the displacement error, is of particular importance as a displacement error in between the positioning coils and the actual location of the target line object is difficult to prevent due to (1) the limitation of the physical alignment of positioning coils and the target line object; and (2) the operation precision of assembly workmanship.
2. Description of the Related Art
Most computer applications nowadays employ a pointing device to perform graphic user interface. The position of an object pointed to can be determined by a prior art mouse or a digitizer depending on the accuracy of positioning required by the applications. On the other hand, there is a lack of apparatus and/or method that can be effectively applied to those applications requiring the recordation of the movement of a line object. Prior art which is disclosed in U.S. Pat. No. 5,355,146 furnishes a similar purpose wherein two mouse roller balls are applied at the bottom of the device for determining the location of a line segment. This prior art, however, has a serious drawback that the position determined is relative to the starting point of a positioning process, not an absolute coordinate to a given referenced space. This limits the use of this device as it can only be moved around a document without lifting the device up for second attempt. The positions determined by two trials will be totally irrelevant and similar to that resulted in the operation of a mouse. Furthermore, positioning errors are usually induced resulting from the slip of the mouse roller balls when they roll over the target document. It is therefore desirable to pursue an effective way and mechanism to resolve the problem of inconsistency among multiple passes of positioning and the problem of positioning errors induced by the sliding friction for those applications requiring more accurate trace of the movement of a line object.
In the fields of desk top publishing, image processing or other types of multimedia applications, a simple to use yet effective image scanning device to input the desired image data for a computer is required. With the increasing demand of the aforesaid applications, an image scanner has become an essential peripheral to computer applications. Conventionally, image scanners are classified into three major categories,--flatbed, sheet-feed and hand-held--, among which the hand-held scanner is most compact and is indeed portable for mobile applications. Hand-held scanners, however, have a number of drawbacks in many respects that mean hand-held scanners can only be employed for low-end applications.
Hand-held scanners are defective in a number of respects. First, they must be carefully moved across a column of a document without the hand-held scanner being twisted as it is drawn across the column. If any twisting motion is introduced into the hand scanning, the resultant computer image will be deformed. Even if the hand-held scanner is carefully moved and uniform motion of the two ends of the hand-held scanner is achieved, the resultant computer image may still be distorted. This is because the roller of the hand-held scanner may slip due to friction between the roller and the target document when the scanner is moving across the document as such the scanned image lines may not be equally spaced. As a result, the resultant image may be shrunk in one area and expanded in others.
Furthermore, if hand-held scanner captures less than all of the material on a document, it is required to move the hand-held scanner back and forth across the document via multiple passes to cover the desired area of the document entirely. However, this requires alignment of the sub-images which are scanned into the computer by different scanning operations of the hand-held scanner. Attempts of making such alignment automatically have been conducted, but none of the prior art, either by hardware or by software, achieves a satisfactory result. Therefore, the sub-images resulted from multiple scans can only be assembled manually by the user through cumbersome editing processes.
Accordingly, it is an object of the present invention to achieve a new hand-positionable data input device for a computer that is simple to use in locating the position of a traceable line object and more flexible and accurate than those known to the prior art and further that overcomes the defects of the prior art. It is also an object of the present invention to achieve a new type of image scanning system that captures image together with the corresponding spatial information relative to a given coordinate system. This results in freehanded manual use of the image scanning device without suffering the defects that are common to the prior art hand-held scanner.